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I recently bought a solar cell rated at 3v and 200mA dc to power a 1.5v dc motor that is used as an air pump for my aquarium.All the 1.5v solar cells available here have low ampere like 50mA or so.

So how can i drop the voltage supplied by the solar cell to 1.5v while doubling the current to 400mA.also is it possible for me to do this with just resistors??I'm a complete Noob here.

Thanks in advance..

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  • \$\begingroup\$ How much current does your motor draw? \$\endgroup\$ Mar 31, 2015 at 16:22
  • \$\begingroup\$ no idea...i dont have a multimeter to find out \$\endgroup\$
    – Kokachi
    Apr 1, 2015 at 9:34

2 Answers 2

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You have another option which may be easier. Buy a second solar panel and wire it in parallel to the first panel. Then you will have 3.0 volts and 400 mA.

When you hook the panels up to your motor, they will just drop to the 1.5 volts that you need. Sounds like magic, but it's the way solar panels work (I use then all the time) and this way might be easier than a voltage regulator.

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  • \$\begingroup\$ hmm..im interested..coz i just happen to have an extra panel with me...could you elaborate more please...i didnt know about that before \$\endgroup\$
    – Kokachi
    Mar 31, 2015 at 10:35
  • \$\begingroup\$ Check out my answer to this question:electronics.stackexchange.com/questions/160507/…. Then look at the OP comment to my answer. He had almost the exact problem as you, with a panel at higher than 24volts, but motor needed 24 volts. One person suggested the same answer as was given to you in the first answer with voltage regulator, but all he needed to do was to hook it up and the voltage of the panel will drop to your mototr's voltage. Check out that answer as I try to explain it there. \$\endgroup\$
    – Filek
    Mar 31, 2015 at 18:51
  • \$\begingroup\$ Whoever gave me a minus 1 doesn't understand how solar panels work. The first answer goes way above what is needed and may not actually work. I use solar panels every day, they have such a negligible resistance the whatever you hook them up to, their voltage drops to the voltage of that device. For example every 12 volt panel is actually 18 volts under full sunlight, but when connected to a 12 volt battery, drops to 12 volts instantly. No voltage regulator needed. \$\endgroup\$
    – Filek
    Mar 31, 2015 at 19:00
  • \$\begingroup\$ If you use the voltage regulator option, you may loose some of your potential current. The regulator would take the 3.0 volt output and whatever current is given at 3.0 volts and convert down to 1.5 volts with a higher current. The problem is that at max voltage, solar panels have a relatively lower current. The max current of a solar panel is closer to 66-75% of its max voltage. So if you parallel the two and run at 1.5 volts it will be 50% of max voltage which won't give you max current (but from what I have seen from the data it won't be that far off), but it would be more than at 3.0v. \$\endgroup\$
    – Filek
    Mar 31, 2015 at 19:10
  • \$\begingroup\$ My above comment is a little inaccurate. At maximum voltage, current will be almost zero, so the voltage regulator won't provide much power. I just looked up the current to voltage curve of solar panels, and any voltage under about 70% should allow for close to maximum current (not maximum power because the voltage is lower), but you want maximum current at the lower voltage. So parallel them and you should be good to go. \$\endgroup\$
    – Filek
    Mar 31, 2015 at 19:23
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Use a voltage regulator.

You won't get exactly half the voltage and double the current. You can get close by using a switching voltage regulator. Texas Instruments has a nice selection that will step down 3V to 1.5V with fairly good efficiency.

For instance the TPS62671 can do this job for you with around 90% efficiency.

Resistor dividers are good for making reference voltages (negligible current draw) or scaling down analog inputs. They're are not good for voltage supplies with high or inconsistent current draw.

A linear regulator would work too, but will not be as efficient as a buck topology.

Note that the specs you gave are for open-circuit voltage and short-circuit current. You will not get both those values at the same time, ever. Using a regulator is the best option you have to provide a constant voltage while adding more panels in parallel on the other side of the regulator is the best way to make sure you can provide enough current.

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  • \$\begingroup\$ i though about using a buck down converter module...unforunately i dont get TI components here...all i can get is cheap ebay buck down converter modules (XL4005 or LM2596) which only have input voltage starting from 4 volts... \$\endgroup\$
    – Kokachi
    Mar 31, 2015 at 10:33

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